Display device and manufacturing method thereof

ABSTRACT

In a semi-transmission liquid crystal display device, two resist masks are required to form a reflective electrode and a transparent electrode; therefore, cost is high. A transparent electrode and a reflective electrode which function as a pixel electrode are stacked. A resist pattern which includes a region having a thick film thickness and a region having a thinner film thickness than the aforementioned region is formed over the reflective electrode by using a light exposure mask which includes a semi-transmission portion. The reflective electrode and the transparent electrode are formed by using the resist pattern. Therefore, the reflective electrode and the transparent electrode can be formed by using one resist mask.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/644,895, filed Jul. 10, 2017, now pending, which is a continuation ofU.S. application Ser. No. 14/819,595, filed Aug. 6, 2015, now U.S. Pat.No. 9,703,140, which is a continuation of U.S. application Ser. No.14/153,163, filed Jan. 13, 2014, now abandoned, which is a continuationof U.S. application Ser. No. 12/730,566, filed Mar. 24, 2010, now U.S.Pat. No. 8,634,044, which is a continuation of U.S. application Ser. No.11/614,809, filed Dec. 21, 2006, now U.S. Pat. No. 7,821,613, whichclaims the benefit of a foreign priority application filed in Japan asSerial No. 2005-378778 on Dec. 28, 2005, all of which are incorporatedby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a semiconductor device including apixel electrode, and particularly to a display device. Moreparticularly, the present invention relates to a semi-transmission typeliquid crystal display device including a reflection region and atransmission region.

2. Description of the Related Art

A display device is divided into a self-light emitting display deviceand a non-light emitting display device. A liquid crystal display deviceis the most typical non-light emitting display device. In general, aliquid crystal display device performs a display by being irradiatedwith light from a backlight because it does not emit light.

In a transmission type liquid crystal display device which uses lightfrom a backlight, although a display image is easy to see in a normalroom, there is a problem that a display image is difficult to see undersunlight. Particularly electronic apparatuses which are frequentlyutilized outdoors such as a camera, a portable information terminal, anda mobile phone are greatly affected by this problem.

A semi-transmission type liquid crystal display device has beendeveloped in order to display a favorable image both indoors andoutdoors. A semi-transmission type liquid crystal display deviceincludes a reflection region and a transmission region in one pixel. Thetransmission region includes a transparent electrode and transmits lightso as to function as a transmission type liquid crystal display device.On the other hand, the reflection region includes a reflective electrodeand reflects light so as to function as a reflection type liquid crystaldisplay device. In this manner, a clear image can be displayed bothindoors and outdoors.

As such a liquid crystal display device, there are a passive matrix typeand an active matrix type. Generally, when manufacturing an activematrix type display device, a wiring which is connected to asemiconductor layer of a thin film transistor (TFT) is formed and aconductive film functioning as a pixel electrode is formed over thewiring.

As a pixel electrode, there are a reflective electrode in a reflectionregion and a transparent electrode in a transmission region. Eachelectrode has a different shape. Therefore, a resist mask for forming areflective electrode and a resist mask for forming a transparentelectrode have been required (for example, refer to Patent Documents 1to 5).

Patent Document 1

-   Japanese Published Patent Application No. 2002-229016

Patent Document 2

-   Japanese Published Patent Application No. 2004-46223

Patent Document 3

-   Japanese Published Patent Application No. 2005-338829

Patent Document 4

-   Japanese Published Patent Application No. 2004-334205

Patent Document 5

-   Japanese Published Patent Application No. 2004-109797

SUMMARY OF THE INVENTION

In a conventional semi-transmission type liquid crystal display device,a resist mask is required for each layer when forming a reflectiveelectrode and a transparent electrode. That is, a resist mask forforming a reflective electrode and a resist mask for etching atransparent electrode and a stacked film are required, and the number ofmanufacturing steps is increased for that. Therefore, manufacturing costof a semiconductor device such as a display device is high andmanufacturing time for forming an electrode pattern is necessarily long.

Therefore, one of the objects of the invention is to reduce the numberof resist masks to be used and reduce manufacturing steps.

One feature of the invention is to provide a display device including atransistor, a transparent electrode which is electrically connected tothe transistor, a reflective electrode which is electrically connectedto the transparent electrode, and a storage capacitor which iselectrically connected to the transistor. At least a part of the storagecapacitor is formed below the reflective electrode. An entire undersurface of the reflective electrode is in contact with a top surface ofthe transparent electrode.

Another feature of the invention is to provide a display deviceincluding a transistor, a transparent electrode which is electricallyconnected to the transistor, and a reflective electrode which iselectrically connected to the transparent electrode. At least one of thetransparent electrode and the reflective electrode has a slit. An entireunder surface of the reflective electrode is in contact with a topsurface of the transparent electrode.

Another feature of the invention is to provide a display deviceincluding a transistor, a transparent electrode which is electricallyconnected to the transistor, a reflective electrode which iselectrically connected to the transparent electrode, and a storagecapacitor which is electrically connected to the transistor. At leastone of the transparent electrode and the reflective electrode has aslit. At least a part of the storage capacitor is formed below thereflective electrode. An entire under surface of the reflectiveelectrode is in contact with a top surface of the transparent electrode.

Another feature of the invention is to provide a display deviceincluding a transistor, a transparent electrode which is electricallyconnected to the transistor, a reflective electrode which iselectrically connected to the transparent electrode, and a storagecapacitor which is electrically connected to the transistor. At least apart of the storage capacitor is formed below the reflective electrode.At least a part of the transistor is formed below the reflectiveelectrode. An entire under surface of the reflective electrode is incontact with a top surface of the transparent electrode.

Another feature of the invention is to provide a display deviceincluding a transistor and a pixel electrode which is electricallyconnected to the transistor. The pixel electrode includes a transparentelectrode and a reflective electrode. An entire under surface of thereflective electrode is in contact with a top surface of the transparentelectrode. A film thickness of the transparent electrode in a region incontact with the reflective electrode is thicker than a film thicknessof the transparent electrode in a region not in contact with thereflective electrode.

In the invention, in the aforementioned structure, the display device isprovided with a liquid crystal layer between the reflective electrodeand an opposite electrode.

Another feature of the invention is to provide a manufacturing methodfor a display device. A transistor is formed over a substrate. Aninsulating film is formed over the transistor. A transparent conductivefilm is formed over the insulating film. A reflective conductive film isformed over the transparent conductive film. A resist pattern whichincludes a region having a thick film thickness and a region having athinner film thickness than the aforementioned region is formed over thereflective conductive film by using a light exposure mask including asemi-transmission portion. A transparent electrode formed of thetransparent conductive film and a reflective electrode formed of thereflective conductive film are formed by using the resist pattern.

Another feature of the invention is to provide a manufacturing method ofa display device. A transistor is formed over a substrate. An insulatingfilm is formed over the transistor. A transparent conductive film isformed over the insulating film. A reflective conductive film is formedover the transparent conductive film. A resist pattern which includes aregion having a thick film thickness and a region having a thinner filmthickness than the aforementioned region is formed over the reflectiveconductive film by using a light exposure mask including asemi-transmission portion. The reflective conductive film and thetransparent conductive film are etched by using the resist pattern. Apart of the resist pattern is removed. The reflective conductive film isetched by using the resist pattern a part of which is removed.

As described above, a transparent electrode and a reflective electrodewhich is in contact with a part of the transparent electrode can beformed by using one resist pattern. Since two patterns of thetransparent electrode and the reflective electrode can be formed byusing one resist pattern, manufacturing steps can be reduced and thedisplay device with low cost can be realized.

Note that in the invention, various kinds of transistors can be appliedand are not limited to a specific transistor. A thin film transistor(TFT) using a non-monocrystalline semiconductor film typified byamorphous silicon or polycrystalline silicon, a transistor formed usinga semiconductor substrate or an SOI substrate, a MOS transistor, ajunction type transistor, a bipolar transistor, a transistor using acompound semiconductor such as ZnO or a-InGaZnO, a transistor using anorganic semiconductor or a carbon nanotube, or other transistors can beused. In addition, the kind of a substrate over which a transistor isprovided is not limited, and a monocrystalline substrate, an SOIsubstrate, a glass substrate, a plastic substrate, or the like can beemployed.

Note that a structure of a transistor is not limited to a specificstructure. For example, a multi-gate structure where the number of gatesis two or more may be employed. Gate electrodes may be provided over andunder a channel. A gate electrode may be provided over or under thechannel. A forward staggered structure or an inverted staggeredstructure may be employed. A channel region may be divided into aplurality of regions, or connected in parallel or in series. A sourceelectrode or a drain electrode may overlap with a channel (or a partthereof). An LDD region (low concentration impurity region) may beprovided.

Note that in the invention, being connected is synonymous with beingelectrically connected. Therefore, in addition to a predeterminedrelation of connection, another element which enables an electricalconnection (for example, a switch, a transistor, a capacitor, a resistorelement, a diode, or the like) may be provided in a structure disclosedin the invention.

Note that a switch shown in the invention is not limited to a specificswitch. An electrical switch or a mechanical switch can be applied. Anyelement which can control a flow of current can be employed. Atransistor, a diode (a PN diode, a PIN diode, a Schottky diode, adiode-connected transistor, or the like), or a logic circuit combinedtherewith may be employed. When a transistor is used as a switch, apolarity (conductivity type) thereof is not specifically limited sincethe transistor is operated as a mere switch. However, in the case whereOFF current is preferably small, a transistor having a polarity withsmaller OFF current is preferably used. As a transistor with small OFFcurrent, a transistor provided with an LDD region, a transistor with amulti-gate structure, or the like may be used. In addition, an n-channeltransistor is preferably used when operating in a state where apotential of a source terminal of the transistor, which operates as aswitch, is close to a low potential side power source (Vss, GND, 0 V, orthe like), whereas a p-channel transistor is preferably used whenoperating in a state where a potential of a source terminal of thetransistor is close to a high potential side power source (Vdd or thelike). This is because the transistor can easily function as a switchsince an absolute value of a gate-source voltage thereof can be made tobe large. Note that a CMOS type switch may also be applied by using bothn-channel and p-channel transistors.

Note that an element provided in a pixel is not limited to a specificdisplay element. A display element provided in a pixel is, for example,a display medium in which contrast is changed by an electromagneticeffect, such as an EL element (an organic EL element, an inorganic ELelement, or an EL element containing an organic compound and aninorganic compound), an electron emitting element, a liquid crystalelement, electronic ink, a grating light valve (GLV), a plasma display(PDP), a digital micromirror device (DMD), a piezoelectric ceramicdisplay, or a carbon nanotube. Note that a display device using an ELelement includes an EL display; a display device using an electronemitting element includes a field emission display (FED), an SED typeflat panel display (Surface-conduction Electron-emitter Display), andthe like; a display device using a liquid crystal element includes aliquid crystal display; and a display device using electronic inkincludes electronic paper.

Note that in the invention, one pixel corresponds to one color element.Therefore, in the case of a full-color display device formed of colorelements of R (red), G (green), and B (blue), the smallest unit of animage is formed of three pixels of an R pixel, a G pixel, and a B pixel.Note that the number of color elements is not limited to three colors,and color elements may be formed of more than three colors such as RGBW(W is white). Note that in the case where a pixel is referred to as onepixel (three colors), three pixels of RGB is considered as one pixel.

Note that in the invention, the case where pixels are arranged in matrixcorresponds to the case where dots of the three color elements arearranged in a so-called delta pattern in the case of performing a fullcolor display with three color elements (for example, RGB), as well asthe case where pixels are arranged in a so-called stripe pattern. Notethat a color element is not limited to three colors and may be more thanthree colors such as RGBW. Further, a region of each dot of a colorelement may have a different size.

Note that a transistor is an element having at least three terminalsincluding a gate electrode, a drain region (or a drain electrode), and asource region (or a source electrode) and includes a channel formingregion between the drain region and the source region. Here, it isdifficult to precisely define the source region and the drain regionsince they depend on a structure, operating conditions, and the like ofthe transistor. Therefore, in this specification, a region whichfunctions as a source region or a drain region is referred to as a firstterminal or a second terminal.

Note that in the invention, a semiconductor device corresponds to adevice having a circuit which includes a semiconductor element (atransistor, a diode, or the like). Further, a semiconductor device maybe a general device which can be operated by using semiconductorcharacteristics. A display device may be a main body of a display panelin which a plurality of pixels including a display element such as aliquid crystal element or an EL element and a peripheral driver circuitfor driving the pixels are formed over a substrate, and may also be amain body of a display panel provided with a flexible printed circuit(FPC) or a printed wiring board (PWB). A light emitting device is adisplay device using particularly a self-light emitting display elementused for an EL element, an electron emitting element, or the like.

According to the present invention, manufacturing steps can be reducedwith respect to conventional art and manufacturing cost of asemiconductor device and a display device can be lowered.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1C are cross sectional views showing a manufacturing step ofa semiconductor device of the invention.

FIGS. 2A to 2C are cross sectional views showing a manufacturing step ofa semiconductor device of the invention.

FIGS. 3A and 3B are cross sectional views showing a manufacturing stepof a semiconductor device of the invention.

FIG. 4 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 5 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 6 is a cross sectional view showing a semiconductor device of theinvention.

FIGS. 7A and 7B are cross sectional views showing a manufacturing stepof a semiconductor device of the invention.

FIGS. 8A and 8B are cross sectional views showing a manufacturing stepof a semiconductor device of the invention.

FIG. 9 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 10 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 11 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 12 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 13 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 14 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 15 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 16 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 17 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 18 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 19 is a cross sectional view showing a semiconductor device of theinvention.

FIGS. 20A to 20C are top plan views showing a light exposure mask, andFIG. 20D is a diagram showing light intensity distribution.

FIG. 21 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 22 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 23 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 24 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 25 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 26 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 27 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 28 is a top plan view showing a semiconductor device of theinvention.

FIG. 29 is a top plan view showing a semiconductor device of theinvention.

FIG. 30 is a top plan view showing a semiconductor device of theinvention.

FIG. 31 is a top plan view showing a semiconductor device of theinvention.

FIG. 32 is a top plan view showing a semiconductor device of theinvention.

FIG. 33 is a top plan view showing a semiconductor device of theinvention.

FIG. 34 is a top plan view showing a semiconductor device of theinvention.

FIG. 35 is a top plan view showing a semiconductor device of theinvention.

FIG. 36 is a top plan view showing a semiconductor device of theinvention.

FIG. 37 is a top plan view showing a semiconductor device of theinvention.

FIG. 38 is a top plan view showing a semiconductor device of theinvention.

FIG. 39 is a top plan view showing a semiconductor device of theinvention.

FIG. 40 is a view illustrating one mode of an electronic apparatus towhich the invention is applied.

FIGS. 41A and 41B are views showing a semiconductor device of theinvention.

FIG. 42 is a view showing a semiconductor device of the invention.

FIG. 43 is a diagram showing a semiconductor device of the invention.

FIGS. 44A to 44H are views illustrating one mode of an electronicapparatus to which the invention is applied.

FIG. 45 is a circuit diagram of a liquid crystal display device of theinvention.

FIG. 46 is a block diagram of a circuit configuration of a liquidcrystal display device of the invention.

FIG. 47 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 48 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 49 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 50 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 51 is a cross sectional view showing a semiconductor device of theinvention.

FIG. 52 is a cross sectional view showing a semiconductor device of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiment modes of the invention are described. Note thatthe present invention can be implemented in various embodiments withinthe range of enablement and it is easily understood by those who areskilled in the art that modes and details herein disclosed can bemodified in various ways without departing from the purpose and thescope of the invention. Therefore, it should be noted that descriptionof embodiment modes is not be interpreted as limiting the invention.Further, any of the embodiment modes to be given below can be combinedas appropriate.

Embodiment Mode 1

Description is made of a manufacturing method for forming a reflectiveelectrode and a transparent electrode with reference to FIGS. 1A to 1Cand 2A to 2C.

First, a conductive film 106 is formed over an insulating film 107 by asputtering method, a printing method, a CVD method, an ink-jet method,or the like. The conductive film 106 may be a transparent conductivefilm or have a reflecting property. In the case of a transparentconductive film, an indium tin oxide (ITO) film in which tin oxide ismixed in indium oxide, an indium tin silicon oxide (ITSO) film in whichsilicon oxide is mixed in indium tin oxide (ITO), an indium zinc oxide(IZO) film in which zinc oxide is mixed in indium oxide, a zinc oxidefilm, a tin oxide film, silicon (Si) containing phosphorus or boron canbe used, for example. Note that IZO is a transparent conductive materialformed by sputtering using a target in which 2 to 20 wt % of zinc oxide(ZnO) is mixed in ITO; however, a composition ratio and the like are notlimited to this.

The conductive film 106 is formed over the insulating film 107, and aconductive film 105 is formed over the conductive film 106. Theconductive film 106 and the conductive film 105 can be formedcontinuously by sputtering, which can reduce the number of steps.

The conductive film 105 is preferably formed from a material with lowresistance or a material with high reflectivity. For example, Ti, Mo,Ta, Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, Ge, or the like,or an alloy thereof can be used. A two-layer structure where theaforementioned materials are stacked may be employed. In this case, astacked layer structure including two layers which uses a metal such asTi, Mo, Ta, Cr, or W, and Al (or an alloy including Al as a maincomponent) may be employed. A stacked layer structure of three layersmay alternatively be employed. In this case, a three-layer structurewhere Al (or an alloy including Al as a main component) is sandwichedbetween metals such as Ti, Mo, Ta, Cr, and W may be employed. Asdescribed above, by arranging a metal such as Ti, Mo, Ta, Cr, or Wadjacent to Al (or an alloy including Al as a main component), a defectcan be decreased when another electrode or another wiring is connected.For example, if an ITO film or the like is connected to Al (or an alloyincluding Al as a main component), a defect such as electric erosionmight happen. Further, if a Si film or the like is in contact with Al(or an alloy including Al as a main component), Al and the Si film mightbe reacted with each other. These problems can be reduced by amultilayer structure.

Note that when an ITO film is used as a conductive film, a step in whichthe ITO film is crystallized by heat treatment is required. In thiscase, it is preferable that the ITO film be formed by sputtering, andafter baking, the conductive film 105 be formed. The number of steps canbe reduced when an ITSO film is used since a step of crystallization isnot required.

After a resist film 104 is formed (applied) over an entire surface ofthe conductive film 105, light exposure is performed using a lightexposure mask shown in FIG. 1A.

In FIG. 1A, a light exposure mask includes a light shielding portion 101a in which exposure light is shielded and a semi-transmission portion101 b in which exposure light partially passes. The semi-transmissionportion 101 b is provided with a semi-transmission film 102 in whichintensity of exposure light is reduced. The light shielding portion 101a is formed to superimpose a metal film 103 over the semi-transmissionfilm 102. A width of the light shielding portion 101 a is referred to ast1, and a width of the semi-transmission portion 101 b is referred to ast2. Here, although an example where the semi-transmission film is usedin the semi-transmission portion, the invention is not limited to this.Any semi-transmission portion is acceptable as long as it can reduceintensity of exposure light. In addition, a diffraction grating patternmay be used for the semi-transmission portion.

That is, a half-tone mask or a gray-tone mask may used for thesemi-transmission portion.

When the resist film is exposed to light using the light exposure maskshown in FIG. 1A, a light-unexposed region and a light-exposed regionare formed. When light exposure is performed, light is passed around thelight shielding portion 101 a or passes through the semi-transmissionportion 101 b; therefore, the exposure region is formed.

When development is performed, the exposure region is removed, and aresist pattern 104 a having two main film thicknesses can be obtainedover the conductive film 105 as shown in FIG. 1B. The resist pattern 104a includes a region having a thick film thickness and a region having afilm thickness thinner than the aforementioned region. The filmthickness of the region having a thin film thickness can be adjusted byadjusting light exposure energy or transmittance of thesemi-transmission film 102.

Next, the conductive film 105 and the conductive film 106 are etched bydry etching. Dry etching is performed by a dry etching apparatus using ahigh density plasma source such as ECR (Electron Cyclotron Resonance) orICP (Inductively Coupled Plasma).

Therefore, a conductive film 105 a and a conductive film 106 a areformed as shown in FIG. 1C.

Here, although an example of using an ICP etching apparatus is shown,the invention is not limited to this, and for example, a parallel platetype etching apparatus, a magnetron etching apparatus, an ECR etchingapparatus, or a helicon-type etching apparatus may also be employed.

Note that the conductive film 105 and the conductive film 106 may beetched by wet etching. However, dry etching is suitable formicrofabrication; therefore, dry etching is preferable. A material forthe conductive film 105 and the conductive film 106 is greatly differentfrom a material for the insulating film 107; therefore, high etchingselectivity of the insulating film 107 with respect to the conductivefilm 105 and the conductive film 106 can be obtained even if dry etchingis performed. At least a top layer of the insulating film 107 may beformed of a silicon nitride film in order to make etching selectivitythereof further high.

In this manner, a pattern formed by stacking the conductive film 106 aand the conductive film 105 a is formed over the insulating film 107 asshown in FIG. 1C.

Next, (a part of) the resist pattern 104 a is ashed or etched (FIG. 2A).In accordance with this step, the region having a thin film thickness inthe resist pattern 104 a is etched and a film thickness of the wholeresist pattern 104 a is decreased by a film thickness of the regionhaving a thin film thickness. Then, a resist pattern 104 b is formed.The resist pattern 104 a is etched in a width direction as well as afilm thickness direction; therefore, a width of the resist pattern 104 bis narrower than widths of the conductive films 105 a and 106 a.Therefore, a side surface of the resist pattern 104 b is not alignedwith a side surface of the conductive film in a lower layer, and theside surface of the resist pattern 104 b is recessed. In FIG. 2B, theresist pattern 104 b is left-right asymmetric.

Next, the conductive film 105 a is etched using the resist pattern 104 bso as to form a conductive film 105 b (FIG. 2B). A material of theconductive film 105 a preferably has high etching selectivity withrespect to the conductive film 106 a in order that the conductive film106 a is not unnecessarily etched simultaneously at this time. Forexample, Ti, Mo, Cr, Al, Nd, or the like or an alloy thereof ispreferably used for the conductive film 105 a, and a stacked layerstructure of the aforementioned materials may be employed. Then, theconductive film 105 b of which pattern is smaller than the conductivefilm 106 a is formed.

Although etching for forming the conductive film 105 b shown in FIGS. 2Aand 2B may be performed by either dry etching or wet etching, FIGS. 2Aand 2B show the case of dry etching. A side surface of the conductivefilm 105 b is formed so as to be generally aligned with the side surfaceof the resist pattern 104 b. One side surface of the conductive film 105b is on the same plane as one side surface of the resist pattern 104 b,and the other side surface thereof corresponds to the other side surfaceof the resist pattern 104 b.

Microfabrication can be realized by performing dry etching. However, theconductive film 106 a is also partially etched when the conductive film105 b is formed.

On the other hand, when the conductive film 105 b is formed by wetetching, etching proceeds isotropically, and the conductive film 105 bsmaller than the resist pattern 104 b is formed. The side surface of theresist pattern 104 b and the side surface of the conductive film 105 bdo not correspond to each other. Therefore, even if the same resistpattern 104 b is used as a mask, the conductive film 105 b is formedsmaller by wet etching than in the case of by dry etching.

Sufficiently high etching selectivity can be obtained by performing wetetching.

When the conductive film 106 a is formed by dry etching, a side surfacethereof has an angle θ₁, which is almost perpendicular or close to 90°with respect to a substrate surface. On the other hand, when theconductive film 105 b is formed by wet etching, the side surface thereofhas an acute angle θ₂ with respect to the substrate surface because ofisotropic etching. Therefore, θ₁>θ₂ is satisfied when the angle θ₁ ofthe side surface of the conductive film 106 a and the angle θ₂ of theside surface of the conductive film 105 b are compared with each other.Note that the angle θ₁ is an inclined angle of the conductive film 106 awith respect to a surface of a substrate (or the insulating film 107),and the angle θ₂ is an inclined angle of the side surface of theconductive film 105 b with respect to the surface of the substrate (orthe insulating film 107). Each of the angles θ₁ and θ₂ is in a range of0 to 90°.

In the case where the conductive film 105 b and the conductive film 106a have a stacked layer structure, an etching rate is different in eachlayer in some cases. Accordingly, the angles formed by the side surfacesof the layers with respect to the substrate surface are different fromeach other in some cases. Therefore, in that case, an angle formed bythe side surface of a film in a lowest layer with respect to thesubstrate surface is denoted by θ₂.

Note that the side surfaces of the conductive film 105 b and theconductive film 106 a are not smooth but uneven in some cases. In thiscase, the angle θ₁ and the angle θ₂ can be determined as appropriate.For example, the angle θ₁ and the angle θ₂ can be determined using arough straight line or curved line drawn with respect to uneven sidesurfaces. Further, a plurality of angles θ₁ and angles θ₂ can becalculated based on uneven side surfaces, and average values thereof canbe taken as the angle θ₁ and the angle θ₂. The most rational method maybe employed.

As described above, the conductive film 105 b is formed by either a dryetching method or a wet etching method. The conductive film 105 b whichincludes the side surface recessed with respect to the side surface ofthe conductive film 106 a can be formed by either one of the etchingmethods. One of factors is that the size of the resist pattern 104 a,which is a mask for forming the conductive film 106 a, and the size ofthe resist pattern 104 b, which is a mask for forming the conductivefilm 105 b, are different from each other, and the resist pattern 104 bis smaller than the resist pattern 104 a.

Subsequently, the resist pattern 104 b is removed (FIG. 2C).Accordingly, an electrode formed of the conductive film 105 b and theconductive film 106 a is formed. The conductive film 106 a and theconductive film 105 b function as a pixel electrode. However, theinvention is not limited to this.

More preferably, the conductive film 105 b is formed of a reflectiveconductive film so as to function as a reflective electrode and theconductive film 106 a is formed of a transparent conductive film so asto function as a transparent electrode. In addition, the conductive film106 a is required to be provided below the conductive film 105 b, and anentire under surface of the conductive film 105 b is in contact with atop surface of the conductive film 106 a.

A reflection portion 108 a is provided with a reflective electrode, anda transmission portion 108 b is provided with a transparent electrode.Therefore, a reflective electrode and a transparent electrode can bemanufactured with a small number of steps, and a semi-transmission typedisplay device can be easily manufactured. Microfabrication is notrequired for a reflective electrode and a transparent electrode.Accordingly, there is no big problem if a reflective electrode and atransparent electrode are slightly misaligned with each other. Forexample, if a reflective electrode is slightly smaller and thetransparent electrode is slightly larger, display is not greatlyaffected. Therefore, manufacturing yield is unlikely to be reduced evenwhen such a manufacturing method is performed, and beneficial effects oncost reduction, reduction in the number of manufacturing days, or thelike can be obtained.

In the case where a stacked layer of the conductive film 105 b and theconductive film 106 a is formed using the resist pattern 104 a of theinvention, which includes regions having different film thicknesses,when the conductive film 105 b is formed, that is, when etching isperformed using the resist pattern 104 b as a mask, a part of a surfaceof the conductive film 106 a is etched to some extent. In particular,when the conductive film 105 b is formed by dry etching, selectivitybetween the conductive film 105 b and the conductive film 106 a in thelower layer is difficult to obtain; therefore, a part of the surface ofthe conductive film 106 a is easily etched. Thus, when a film thicknessa of the conductive film 106 a (a film thickness of the conductive film106 a in a portion where a top surface thereof is in contact with theconductive film 105 b) and a film thickness b (a film thickness of theconductive film 106 a in a portion where a top surface thereof is not incontact with the conductive film 105 b) are compared with each other inFIG. 2C, the film thickness a <the film thickness b is satisfied. Notethat the film thickness a refers to an average film thickness of theconductive film 106 a in a portion which is not overlapped with theconductive film 105 b, and the film thickness b refers to an averagefilm thickness of the conductive film 106 a in a portion which isoverlapped with the conductive film 105 b.

The side surface of the conductive film 105 b formed in this embodimentmode is inclined in some cases. Therefore, in the case where theconductive film is used for a liquid crystal display device, rubbing canbe smoothly performed to the side surface of the conductive film 105 bwhen rubbing is performed from the inclined surface side of theconductive film 105 b. When rubbing is performed from a direction wherethe side surface of the conductive film 105 b is perpendicular, rubbingis incomplete because of stress on a rubbing cloth in a perpendicularside surface portion, and orientation is incomplete in some cases.Therefore, rubbing is preferably performed from a side where the sidesurface of the conductive film 105 b is inclined.

In addition, in the case where the conductive film 105 b of which bothside surfaces are inclined is formed by wet etching, rubbing can besmoothly performed from both directions, which is more effective.

Note that as shown in FIGS. 1A and 1B, a resist, of which partirradiated with light is dissolved, is referred to as a positive typeresist. However, it is not limited to a positive type resist, and anegative type resist may be used. A negative type resist is a resist, ofwhich part not irradiated with light is dissolved.

FIGS. 3A and 3B show views in the case of using a negative type resist.FIG. 1A corresponds to FIG. 3A, and FIG. 1B corresponds to FIG. 3B.Other than that, there are few differences between positive type andnegative type. As shown in FIG. 3A, a transparent portion 101 c isprovided above a part of a resist 304 which is expected to be left. Thelight shielding portion 101 a is provided above a part of the resist 304which is expected to be removed. The semi-transmission portion 101 b isprovided above a part of the resist 304, a small portion of which isexpected to be left. As a result, as shown in FIG. 3B, a resist 304 a isformed.

Description is made with reference to various drawings in thisembodiment mode. One drawing consists of various components. Therefore,another structure can be made by combining each of the components fromeach drawing.

Embodiment Mode 2

In Embodiment Mode 1, description is made of the case where a pixelelectrode is formed over the insulating film 107. However, actually apixel electrode is connected to another wiring, transistor, storagecapacitor, or the like. Therefore, if required, the insulating film 107is provided with a contact hole so that the pixel electrode is connectedto a wiring or the like.

Thus, FIG. 4 shows a cross sectional view of that case. An insulatingfilm 107 a is provided with a contact hole 402. A wiring 401 is formedbelow the contact hole 402. The wiring 401 is connected to one of asource or a drain of a transistor in many cases. Alternatively, in manycases, the wiring 401 itself is one of the source or the drain of thetransistor, or an electrode of a storage capacitor.

In this case, the conductive film 106 a is required to be formed belowthe conductive film 105 b since the manufacturing method described inEmbodiment Mode 1 is used. Therefore, the conductive film 105 b is alsoformed over the conductive film 106 a which is formed so as to cover thecontact hole 402.

A transistor, a wiring, and a storage capacitor are formed below theconductive film 105 b. In the case where the conductive film 105 b is areflective electrode and the conductive film 106 a is a transparentelectrode, a transmission region is preferably made as large as possiblesince it is where light is transmitted in order to perform display. Onthe other hand, in a reflection region, display is not affected evenwhen some element is provided below the reflective electrode. Therefore,a transistor, a wiring, and a storage capacitor are formed below theconductive film 105 b, so that a layout can be efficiently designed.

Note that although the whole area of the transistor and the storagecapacitor is preferably formed below the reflective electrode, theinvention is not limited to this. A part of the transistor and thestorage capacitor may be formed on the outside of the reflectiveelectrode (the outside of the reflection region).

Next, description is made of unevenness of the reflective electrode. Thereflective electrode is provided to reflect external light in order toperform display. External light is preferably diffusely reflected by thereflective electrode in order to utilize external light entering thereflective electrode efficiently and improve display luminance.

Here, as shown in FIG. 5, an insulating film 107 b may be provided withunevenness 501, so that the reflective electrode can be made uneven.Note that the insulating film 107 b may have a stacked layer structure.Further, as shown in FIG. 6, a contact hole 501 a may be used forforming unevenness. In this case, the contact hole 501 a functions toconnect the wiring 401 and the conductive film 106 a as well.

Next, an example of a forming method of unevenness of the insulatingfilm and the reflective electrode is shown. In FIGS. 1A to 1C and 3A and3B, description is made of a method for forming the resist by using thelight exposure mask including the light shielding portion 101 a in whichexposure light is shielded and the semi-transmission portion 101 b inwhich exposure light partially passes. This manufacturing method may beapplied to a method for forming unevenness of the insulating film andthe reflective electrode; and a contact hole in the insulating film witha small number of steps. Therefore, further reduction in the number ofsteps can be realized.

In addition, production equipment is already available since thismanufacturing method is used for forming the transparent electrode andthe reflective electrode. Therefore, there is no special requirement forusing this manufacturing method in order to form unevenness of thetransparent electrode and the reflective electrode. Accordingly, it isgreatly advantageous to form both the transparent electrode and thereflecting electrode and the unevenness thereof by this manufacturingmethod.

There is no big problem if the unevenness is slightly misaligned.Microfabrication is not required for the unevenness. Therefore, theunevenness can be manufactured without reducing manufacturing yield.

In FIG. 7A, a light exposure mask includes a light shielding portion 701a in which exposure light is shielded, a semi-transmission portion 701 bin which exposure light partially passes, and a transparent portion 701c in which exposure light passes. The semi-transmission portion 701 b isprovided with a semi-transmission film 702, which reduces intensity ofexposure light. The light shielding portion 701 a is formed bysuperimposing a metal film 703 over the semi-transmission film 702.Here, although an example where the semi-transmission film is used forthe semi-transmission portion is described, the invention is not limitedto this. The semi-transmission portion is acceptable as long as itreduces intensity of exposure light. Further, a diffraction gratingpattern may be used for the semi-transmission portion.

An electrode 705 is provided over an insulating film 707. A film 704which is sensitive to light (for example, photosensitive acryl) isprovided thereover. When the film 704 is exposed to light by using thelight exposure mask shown in FIG. 7A, a light-unexposed region, alight-exposed region, and a semi light-exposed region are formed. A partof the film 704 which is irradiated with light is removed, therebyforming a film 704 a as shown in FIG. 7B, and a contact hole 706 a andunevenness 706 are formed simultaneously.

Note that although the unevenness other than the contact hole is formedin FIGS. 7A and 7B, the invention is not limited to this. A plurality ofholes such as contact holes may be formed in order to form unevenness.In this case, a wiring is not required to be provided below the holessince an electrical connection is not necessarily required. In the casewhere there is no electrical problem, a wiring may be provided.

Note that although a part of the film 704 which is irradiated with lightis removed in FIGS. 7A and 7B, the invention is not limited to this. Onthe contrary, a part of the film 704 which is not irradiated with lightmay be removed.

Note that although a resist is not used in FIGS. 7A and 7B, theinvention is not limited to this. Unevenness and a contact hole may beformed by dry etching or wet etching using a resist after forming afilm.

Note that a thickness (a cell gap) of a liquid crystal in thetransmission region is made thicker than a thickness of a liquid crystalin the reflection region in some cases. This is because light passestwice in the reflective region, while light passes only once in thetransmission region. A cell gap in the transmission region may be madethicker by adjusting the cell gap. FIGS. 8A and 8B show that case. Thefilm 704 is removed so as to form a film 704 b; therefore, a depressedportion 801 in the transmission region as well as a contact hole can beformed. A cell gap in the depressed portion 801 becomes thick.Therefore, this part may be used as a transmission region.

In this case, no additional step is required for thickening a cell gap;therefore, cost can be reduced.

Note that this embodiment mode shows an example in the case where a partof the description in Embodiment Mode 1 is transformed. Therefore, thedescription in Embodiment Mode 1 can be applied to this embodiment modeor combined with this embodiment mode.

In addition, description is made with reference to various drawings inthis embodiment mode. One drawing consists of various components.Therefore, another structure can be made by combining each of thecomponents from each drawing.

Embodiment Mode 3

Next, description is made of a specific example in the case where atransistor is provided. Note that a transistor is not necessarilyrequired and a so-called passive matrix type can also be applied.

First, description is made of a method for forming a top gate type TFTover a substrate 901 with reference to FIG. 9. The substrate 901 is asubstrate having a light transmitting property, such as a quartzsubstrate, a glass substrate, or a plastic substrate. Note that thesubstrate 901 may be a substrate having a light shielding property, anda semiconductor substrate or an SOI (Silicon On Insulator) substrate maybe used.

An insulating film 902 is formed over the substrate 901 as a base film.As the insulating film 902, a single layer of an insulating film such asa silicon oxide film, a silicon nitride film, or a silicon oxynitride(SiO_(x)N_(y)) film; or a stacked layer of at least two films of theaforementioned films is used.

Note that a silicon oxide film is preferably used for a part in contactwith a semiconductor. As a result, an electron trap in the base film orhysteresis in transistor characteristics can be suppressed. Further, atleast one film containing a large amount of nitrogen is preferablyprovided as the base film; therefore, impurities from glass can bereduced.

Next, an island-shaped semiconductor film 903 is formed over theinsulating film 902.

The island-shaped semiconductor film 903 is formed by forming asemiconductor film over an entire surface of the insulating film 902 bya sputtering method, an LPCVD method, a plasma CVD method, or the like,and subsequently processing the shape of the semiconductor film using amask which is formed by a photolithography method or the like. When theisland-shaped semiconductor film 903 is formed of a crystallinesemiconductor film, there are a method for forming a crystallinesemiconductor film directly over the substrate 901; and a method inwhich an amorphous semiconductor film is formed over the substrate 901and is thereafter crystallized by heat treatment so as to form acrystalline semiconductor film. As for heat treatment in crystallizationfor the latter method, a heating furnace, laser irradiation, irradiationwith light emitted from a lamp instead of laser light (hereinafterreferred to as lamp annealing), or a combination thereof is employed.

A crystalline semiconductor film may be formed by a thermalcrystallization method in which nickel or the like is added to anamorphous semiconductor film, and subsequently, the aforementioned heattreatment is performed. Note that when the crystalline semiconductorfilm is obtained by performing crystallization by a thermalcrystallization method using nickel, gettering treatment in which nickelis removed is preferably performed after crystallization.

When the crystalline semiconductor film is formed throughcrystallization by laser irradiation, a continuous wave (CW) laser beamor a pulsed laser beam (a pulse laser beam) can be used. As a usablelaser beam, a beam emitted from one or plural kinds of the followinglasers can be used: a gas laser such as an Ar laser, a Kr laser, or anexcimer laser; a laser using single crystalline YAG, YVO₄, forsterite(Mg₂SiO₄), YAlO₃, or GdVO₄, or polycrystalline (ceramic) YAG, Y₂O₃,YVO₄, YAlO₃, or GdVO₄ as a medium, doped with one or more of Nd, Yb, Cr,Ti, Ho, Er, Tm, and Ta as a dopant; a glass laser; a ruby laser; analexandrite laser; a Ti:sapphire laser; a copper vapor laser; and a goldvapor laser. Crystals with a large grain size can be obtained byirradiation with a laser beam having a fundamental wave of such a laserbeam or second to fourth harmonic waves thereof. For example, the secondharmonic wave (532 nm) or the third harmonic wave (355 nm) of an Nd:YVO₄laser (fundamental wave is 1064 nm) can be used. This laser can beemitted by a CW or a pulsed oscillation. When emitted by a CW laser, thepower density of the laser of approximately 0.01 to 100 MW/cm²(preferably 0.1 to 10 MW/cm²) is required. The irradiation is performedat a scanning rate of approximately 10 to 2000 cm/sec.

Note that a laser using single crystalline YAG, YVO₄, forsterite(Mg₂SiO₄), YAlO₃, or GdVO₄; or polycrystalline (ceramic) YAG Y₂θ₃, YVO₄,YAlO₃, or GdVO₄ as a medium, doped with one or more of Nd, Yb, Cr, Ti,Ho, Er, Tm, and Ta as a dopant; an Ar ion laser; or a Ti:sapphire lasercan be continuously oscillated. Further, pulse oscillation thereof canbe performed at a repetition rate of equal to or more than 10 MHz bycarrying out Q-switch operation or mode locking. When a laser beam isoscillated at a repetition rate of equal to or more than 10 MHz, asemiconductor film is irradiated with a next pulse while thesemiconductor film is melted by the laser beam and solidified.Accordingly, unlike in the case of using a pulsed laser with a lowrepetition rate, a solid-liquid interface can be continuously moved inthe semiconductor film; therefore, crystal grains which continuouslygrow in a scanning direction can be obtained.

When ceramic (polycrystal) is used as a medium, the medium can be formedto have a free shape in a short time at low cost. When a single crystalis used, a columnar medium with several mm in diameter and several tensof mm in length is usually used. In the case of using ceramic, a mediumcan be made much larger.

Concentration of a dopant such as Nd or Yb in a medium, which directlycontributes to a light emission, cannot be changed largely in both ofthe single crystal and the polycrystal; therefore, there is a limitationto some extent in improvement in output of a laser by increasing theconcentration. However, in the case of the ceramic, the size of a mediumcan be made significantly large as compared with the single crystal;therefore, drastic improvement in output of a laser can be realized.

Further, in the case of the ceramic, a medium with a parallelepipedshape or a rectangular parallelepiped shape can be easily formed. When amedium having such a shape is used and oscillated light is made totravel in a zigzag manner inside the medium, a path of the oscillatedlight can be made long. Therefore, amplitude is increased and a laserbeam can be oscillated at a high output. Furthermore, a cross section ofa laser beam, which is emitted from a medium having such a shape, is aquadrangular shape; therefore, as compared with a laser beam with acircular shape, the laser beam with the quadrangular shape in crosssection has an advantage to be formed into a linear beam. By shaping alaser beam emitted in the aforementioned manner using an optical system,a linear beam with 1 mm or less in length of a shorter side and severalmm to several m in length of a longer side can be easily obtained. Inaddition, a medium is uniformly irradiated with excited light, so that alinear beam is emitted with uniform energy distribution in a long sidedirection.

By irradiating the semiconductor film with such a linear beam, an entiresurface of the semiconductor film can be more uniformly annealed. In thecase where uniform annealing is required from one end to the other endof the linear beam, ingenuity such as arrangement of slits on both endsof the linear beam so as to shade an attenuated portion of energy fromlight is required.

When the semiconductor film is annealed using a linear beam with uniformintensity obtained in the aforementioned manner and an electronicapparatus is manufactured using this semiconductor film, characteristicsof the electronic apparatus are favorable and uniform.

Next, if necessary, the semiconductor layer is doped with a very smallamount of an impurity element (boron or phosphorus) in order to controla threshold value of a TFT. Here, an ion doping method is used, in whichplasma excitation is performed without mass separation of diborane(B₂H₆). However, mass separation may be performed so as to preciselycontrol the amount of dopant. Therefore, a threshold voltage can beprecisely controlled.

The island-shaped semiconductor film 903 is formed to have a thicknessof 25 to 80 nm (preferably 30 to 70 nm). Although a material for thesemiconductor film is not limited, the semiconductor film is preferablyformed from silicon, a silicon-germanium (SiGe) alloy, or the like.

Next, a gate insulating film 904 is formed so as to cover theisland-shaped semiconductor film 903. As the gate insulating film 904, asingle layer structure or a stacked layer structure of a thermal oxidefilm, a silicon oxide film, a silicon nitride film, a silicon oxynitridefilm, or the like can be used. A silicon oxide film is preferably usedfor the gate insulating film which is in contact with the island-shapedsemiconductor film 903. This is because a trap level at an interfacebetween the gate insulating film and the island-shaped semiconductorfilm can be lowered. Further, when a gate electrode is formed from Mo, asilicon nitride film is preferably used for the gate insulating filmwhich is in contact with the gate electrode. This is because Mo is notoxidized by a silicon nitride film.

Here, as the gate insulating film 904, a silicon oxynitride film(composition ratio: Si=32%, 0=59%, N=7%, and H=2%) having a thickness of115 nm is formed by a plasma CVD method.

Next, a conductive layer is formed over the gate insulating film 904 andthe shape of the conductive layer is processed using a mask formed by aphotolithography method or the like so as to form a gate electrode 908and a gate wiring. A wiring and an electrode for a storage capacitor maybe formed as well. As a material for these conductive layer, Ti, Mo, Ta,Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, Ge, or the like, analloy of these elements, or the like is used. Alternatively, a stackedlayer structure of the aforementioned elements or an alloy thereof maybe used. Here, the gate electrode is formed from Mo. Mo is preferablebecause it can be easily etched and is resistant to heat. Next, theisland-shaped semiconductor film 903 is doped with an impurity elementusing the gate electrode 908 or a resist as a mask in order to form achannel forming region and impurity regions functioning as a sourceregion and a drain region.

At this time, an LDD region may be formed.

Next, an insulating film 917 is formed using an inorganic materialhaving a light transmitting property (silicon oxide, silicon nitride,silicon oxynitride, or the like), an organic compound material having alow dielectric constant (a photosensitive or nonphotosensitive organicresin material), or a stacked layer thereof. Alternatively, theinsulating film 917 (or a part thereof) may be formed using a materialcontaining siloxane. Siloxane is a material including a skeleton formedby a bond of silicon (Si) and oxygen (O) and includes an organic groupcontaining at least hydrogen (such as an alkyl group or an aromatichydrocarbon) as a substituent. Alternatively, a fluoro group may be usedas the substituent. Further alternatively, a fluoro group and an organicgroup containing at least hydrogen may be used as the substituent. Theinsulating film 917 may have a stacked layer structure.

Next, a mask is formed of a resist by using a photomask. The insulatingfilm 917 and the gate insulating film 904 are selectively etched usingthe mask so as to form a contact hole. Then, the mask made of a resistis removed.

A conductive film is formed over the insulating film 917 by a sputteringmethod, a printing method, a CVD method, or an ink jet method. The shapeof the conductive film is processed using a mask formed by aphotolithography method or the like so as to form a drain electrode 909,a source electrode, and a source wiring. As for a material, Ti, Mo, Ta,Cr, W, Al, Nd, Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, Ge, or the like, analloy of these elements, or the like is used. Alternatively, the drainelectrode 909 or the like may have a stacked layer structure of theaforementioned elements or an alloy thereof. Here, the drain electrodeand the source wiring are formed to have a three-layer structure where alayer of Al is interposed between layers of Mo.

The drain electrode 909 corresponds to the wiring 401 in FIGS. 4 and 6and the electrode 705 in FIGS. 7A, 7B, 8A, and 8B.

An insulating film 907 is formed thereover. The insulating film 907 isoften formed using an organic material since it preferably has highplanarity and good coverage. Note that the insulating film 907 may havea multilayer structure where an organic material is formed over aninorganic material (silicon oxide, silicon nitride, silicon oxynitride,or the like). The insulating film 907 corresponds to the insulating film107 in FIGS. 1A to 1C, 2A to 2C, 3A and 3B.

After a contact hole is formed in the insulating film 907, a conductivefilm is formed thereover by a sputtering method, a printing method, aCVD method, or an ink-jet method.

A conductive film 906 in FIG. 9 corresponds to the conductive film 106 ain FIGS. 2C and 4 to 6. A conductive film 905 in FIG. 9 corresponds tothe conductive film 105 b in FIGS. 4 to 6.

The conductive film 906 is a part of a pixel electrode and is atransparent electrode which transmits light. The conductive film 905 isa part of the pixel electrode and is a reflective electrode whichreflects light. An entire under surface of the reflective electrode isin contact with a top surface of the transparent electrode.

As for the transparent electrode, for example, an indium tin oxide (ITO)film in which tin oxide is mixed in indium oxide, an indium tin siliconoxide (ITSO) film in which silicon oxide is mixed in indium tin oxide(ITO), an indium zinc oxide (IZO) film in which zinc oxide is mixed inindium oxide, a zinc oxide film, a tin oxide film, or the like can beused. Note that IZO is a transparent conductive material formed by asputtering method using a target in which 2 to 20 wt % of zinc oxide(ZnO) is mixed in ITO. However, the invention is not limited to this.

As for the reflective electrode, for example, Ti, Mo, Ta, Cr, W, Al, Nd,Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, Ge, or the like, an alloy thereof,or the like can be used. A two-layer structure where Al is stacked withTi, Mo, Ta, Cr or W; or a three-layer structure where a layer of Al isinterposed between layers of a metal such as Ti, Mo, Ta, Cr, or W may beemployed.

The conductive film 905 and the conductive film 906 are formed by themethod described in Embodiment Modes 1 and 2.

Although not shown in the figure, an alignment film is often formed overthe conductive film 905 and the conductive film 906.

A color filter 916, a black matrix 915, a planarizing film 912, anopposite electrode 914, and the like are formed over an oppositesubstrate 911. A liquid crystal layer 910 is provided between theopposite substrate 911 and the substrate 901.

In a part (reflection portion) 920 where light is reflected in orderthat display is performed, light passes through the liquid crystal layer910 twice. That is, external light enters the liquid crystal layer 910from an opposite substrate side, is reflected by the conductive film905, passes the liquid crystal layer 910 again, and goes out from theopposite substrate side; therefore, light passes the liquid crystallayer 910 twice.

On the other hand, in a part (transmission portion) 921 where light istransmitted in order that display is performed, light enters the liquidcrystal layer 910 through the conductive film 906 and goes out from theopposite substrate. That is, light passes through the liquid crystallayer 910 once.

Since the liquid crystal layer 910 has refractive index anisotropy,polarization of light is changed in accordance with a distance traveledby the light in the liquid crystal layer 910, and thereby when an imageis displayed, display is not performed appropriately. Therefore,polarization of light is required to be adjusted. As a method foradjusting polarization of light, a thickness (so-called cell gap) of theliquid crystal layer 910 in the part (reflection portion) 920 wherelight is reflected in order that display is performed may be made thin;therefore, the distance cannot be too long for light to pass the liquidcrystal layer 910 twice.

A film for adjusting a thickness (a film for adjusting a cell gap, alsoreferred to as a thickness adjusting film, a cell gap adjusting film orthe like) may be provided in order to thin the thickness (so-called cellgap) of the liquid crystal layer 910. The film corresponds to aninsulating film 913 in FIG. 9. That is, the insulating film 913 isprovided for adjusting the thickness of the liquid crystal layer in thepart (reflection portion) 920 where light is reflected in order thatdisplay is performed. By providing the insulating film 913, thethickness of the liquid crystal layer in the reflection portion 920 canbe made thinner than a thickness of the liquid crystal layer in thetransmission portion 921.

Note that the thickness of the liquid crystal layer 910 in thereflection portion 920 is preferably half the thickness of the liquidcrystal layer 910 in the transmission portion 921. Here, “half” mayinclude a difference unrecognized by a human eye.

Light does not enter only from a direction perpendicular to thesubstrate, that is, a normal direction. Light often enters obliquely. Byputting these cases together, a distance traveled by the light in thereflection portion 920 may be made substantially approximately the sameas a distance traveled by the light in the transmission portion 921.Therefore, the thickness of the liquid crystal layer 910 in thereflection portion 920 is preferably equal to or more than one third ofthe thickness of the liquid crystal layer 910 in the transmissionportion 921 and equal to or less than two thirds thereof.

As described above, the film for adjusting a thickness is easily formedby being provided on the opposite substrate 911 side. The film foradjusting a thickness is preferably formed using an organic materialsuch as acrylic or polyimide.

Note that light scattering particles may be mixed in the film foradjusting a thickness. Therefore, light is scattered and luminance canbe improved. The light scattering particles are formed of a materialhaving a refractive index different from that of a cell gap adjustingfilm and formed from a resin material having a light transmittingproperty. A film for adjusting a cell gap may be formed so as to containsuch light scattering particles.

Note that the opposite electrode 914 is preferably formed over theinsulating film 913 (a side near the liquid crystal layer 910).Therefore, a sufficiently high electric field can be applied to theliquid crystal layer 910.

However, the invention is not limited to this. As shown in FIG. 10, aninsulating film 1013 may be formed over an electrode 1014 (a side nearthe liquid crystal layer 910). Disconnection of the electrode 1014 canbe prevented since the insulating film 1013 is very thick.

Note that although in FIG. 9, the reflective electrode is not providedwith unevenness in the reflection portion 920, unevenness may be formedas shown in FIGS. 5 and 6. This case is shown in FIG. 10. Unevenness maybe formed by the method described in FIGS. 7A and 7B. Light can bediffused by unevenness 1001 and a contact hole 1001 a.

Note that although a thickness adjusting film is provided on theopposite substrate side in FIGS. 9 and 10, the invention is not limitedto this. The thickness adjusting film may be provided on a side where atransistor is formed. This case is shown in FIG. 11. A part of aninsulating film 907 a is removed to form the thickness adjusting film.Note that FIG. 10 may be combined with FIG. 11. An example of this caseis shown in FIG. 12. A depressed portion 1101 corresponds to thedepressed portion 801 in FIG. 8B. As described above, the depressedportion 1101 is provided in the transmission portion 921; therefore, acell gap in the transmission portion 921 can be made larger than a cellgap in the reflection portion 920.

Note that both of a depressed portion and a thickness adjusting film maybe provided. Both may serve to control a thickness; therefore, eachthickness is not required to be made very large, which leads to easymanufacturing.

Note that although in FIG. 11, a part of the insulating film 907 a isremoved in order to form the depressed portion 1101, the invention isnot limited to this. Other insulating films may be removed. For example,FIG. 50 shows the case where a part of an insulating film 917 a as wellas the insulating film 907 a is removed. Therefore, a difference in cellgaps between the reflection portion 920 and the transmission portion 921can be easily made. As compared with the case where only the insulatingfilm 907 a is removed, a thickness of the insulating film 907 a can bemade thinner, and thereby deficiency such as a warp of the substrate canbe reduced.

FIG. 51 shows the case where an insulating film 902 e, a gate insulatingfilm 904 e, a substrate 901 e, and the like are further partiallyremoved. The insulating film 902 e, the gate insulating film 904 e, thesubstrate 901 e, and the like are formed from films having similarcomponents in some cases; therefore, a depressed portion 1101 c can beformed more deeply.

Note that unevenness may be formed using a contact hole. This case isshown in FIG. 13. Unevenness is formed using a contact hole 1301provided in a part where the conductive film 906 is not connected to thedrain electrode 909. A plurality of contact holes 1301 are formed inorder that surfaces of a wiring and an electrode are made uneven, butnot in order to connect wirings. Note that in the contact hole 1301,similarly in the contact hole 1001 a, the conductive film 906 may be incontact with the drain electrode 909.

FIG. 14 shows the case where the depressed portion 1101 is provided inthe case of FIG. 13.

As described above, there are a plurality of methods for each ofpresence of unevenness, a forming method of unevenness, and an adjustingmethod of a cell gap (thickness adjustment is performed on an oppositesubstrate side or a TFT substrate side). Therefore, any of them may beselected and combined.

Note that in the case where the conductive film 905 is a reflectiveelectrode, a transistor, a wiring, and a storage capacitor arepreferably formed below the conductive film 905. In the case where theconductive film 905 is a reflective electrode and the conductive film906 is a transparent electrode, the transmission region is preferablyprovided as large as possible. This is because light is transmittedthrough the transmission region in order that display is performed. Onthe other hand, in the reflection region, display is not affected evenwhen some element is provided below the reflective electrode. Therefore,a transistor, a wiring, and a storage capacitor are provided below theconductive film 905, and thereby layout can be efficiently designed.

Note that although the whole area of the transistor and the storagecapacitor is preferably provided below the reflective electrode, theinvention is not limited to this. A part of the transistor or thestorage capacitor may be provided outside the reflective electrode(outside the reflection portion).

FIGS. 47 and 48 show cross sectional views in the case where thetransistor and the storage capacitor are provided below the reflectiveelectrode. In FIG. 47, one electrode of a storage capacitor 4701 isformed using a part of a semiconductor layer which is used as an activelayer for a transistor 4702. In FIG. 47, the storage capacitor 4701 isformed between the island-shaped semiconductor film 903 and a storagecapacitor wiring 908 e using the gate insulating film 904 as aninsulator; and between a part of the drain electrode 909 and the storagecapacitor wiring 908 e using the insulating film 917 as an insulator. InFIG. 48, a storage capacitor 4801 is formed between a storage capacitorwiring 908 f and a semiconductor layer 903 f other than thesemiconductor layer used as an active layer for the transistor 4702,using the gate insulating film 904 as an insulator. The semiconductorlayer 903 f is connected to the drain electrode 909 through a contacthole.

Note that although an insulating film is provided over the drainelectrode in FIGS. 9 to 14, and 47 and 48, the invention is not limitedto this. A transparent electrode 906 a may be provided below a drainelectrode 905 a functioning as a reflective electrode, and a pixelelectrode may be provided over an insulating film 1517 which is formedover the gate electrode. This case is shown in FIG. 15. Note that in thecase of FIG. 15, a surface of a reflective electrode may also be madeuneven, or a thickness adjusting film and a depressed portion may beformed to adjust a cell gap. As an example, FIG. 16 shows the case whereunevenness of a reflective electrode is formed using contact holes 1601and 1601 a.

Note that although each of FIGS. 9 to 16 and 47 and 48 shows the casewhere the gate electrode is provided over a channel, that is, the caseof a so-called top gate type transistor, the invention is not limited tothis. The invention can also be applied to the case where a gateelectrode is provided below a channel, that is, the case of a so-calledbottom gate type transistor.

FIG. 17 shows the case of a bottom gate type transistor. A gateinsulating film 1704 is formed over a gate electrode 1708. Anisland-shaped semiconductor film 1703 is formed thereover. An insulatingfilm 1717 is formed thereover. A contact hole is formed, over which adrain electrode 1709 and a source signal line are formed. A structureover the drain electrode 1709 and the source signal line is similar tothe case of a top gate structure. Therefore, in the case of a bottomgate type transistor, a surface of a reflective electrode may also bemade uneven, or a thickness adjusting film and a depressed portion maybe formed to adjust a cell gap. Unevenness of a reflective electrode maybe formed using a contact hole.

Note that this embodiment mode shows an example in the case where thedescription in Embodiment Modes 1 and 2 is concretely realized.Therefore, the description in Embodiment Modes 1 and 2 can also beapplied to this embodiment mode or combined with this embodiment mode.

In addition, description is made with reference to various drawings inthis embodiment mode. One drawing consists of various components.Therefore, another structure can be made by combining each of thecomponents from each drawing.

Embodiment Mode 4

The liquid crystal layer 910 can be provided with liquid crystalmolecules of various modes.

A TN (Twisted Nematic) liquid crystal is taken as an example. When theTN liquid crystal is used, a pixel electrode is not required to beprovided with a slit. That is, the pixel electrode can be provided allover one pixel. A common electrode formed over an opposite substrate canbe formed over all pixels. Therefore, the pixel electrode (thetransparent electrode and the reflective electrode) described inEmbodiment Modes 1 to 3 can be used.

As a liquid crystal other than the TN liquid crystal, there are an MVA(Multi-domain Vertical Alignment) mode and a PVA (Patterned VerticalAlignment) mode in which liquid crystal molecules are arranged in avertical direction. In the case of an MVA mode or a PVA mode, in orderto control tilt of liquid crystal molecules, a pixel electrode isprovide with a slit or divided so as to be arranged at intervals, or aprojection is provided.

FIG. 18 is a cross sectional view in the case where the pixel electrodeis provided with a slit. As shown in FIG. 18, a structure where anopposite electrode is also provided with a slit or the like is the PVAmode. As shown in FIG. 19, a structure where an opposite electrode isprovided with projections 1901 and 1902 is the MVA mode.

When a manufacturing method of the invention is used, a side surface ofa conductive layer 906 b and a side surface of a conductive film 905 bare not aligned with each other. The side surface of the conductive film905 b is recessed with respect to the side surface of the conductivelayer 906 b. An entire under surface of a reflective electrode is incontact with a top surface of a transparent electrode. This is caused bya manufacturing method of the invention, such as the shape of a resistwhich is used when each conductive layer is etched.

Viewing angle characteristics are improved by using the MVA mode or thePVA mode. Therefore, visibility is improved and an image with less colorunevenness even when seen from any angle can be displayed. Further,luminance in a black state can be made extremely low since a normallyblack mode can be used. Therefore, a contrast ratio can be improved.

Note that this embodiment mode shows an example in the case where thedescription in Embodiment Modes 1 to 3 is concretely realized.Therefore, the description in Embodiment Modes 1 to 3 can be applied tothis embodiment mode or combined with this embodiment mode.

In addition, description is made with reference to various drawings inthis embodiment mode. One drawing consists of various components.Therefore, another structure can be made by combining each of thecomponents from each drawing.

Embodiment Mode 5

Next, description is made of the case of a transistor using amorphoussilicon. Note that as for a TFT described in this embodiment mode,Embodiment Modes 1 to 4 can be referred to for the kind of a substrate,a forming method, a material of each layer, and the like.

Also in the case of a transistor using amorphous silicon, a bottom gatetype (inversed staggered type) transistor, a top gate type (staggeredtype) transistor, and the like can be realized. Here, description ismade of the case of using an inversed staggered type transistor.

FIG. 21 is a cross sectional view. An insulating film is formed over asubstrate 2101 as a base film. Note that a base film is not required tobe provided. Next, a conductive layer is formed over the insulating filmor the substrate 2101 and the shape thereof is processed using a maskformed by a photolithography method or the like so as to form a gateelectrode 2108 and a gate wiring. A storage capacitor wiring and anelectrode may be formed as well.

A gate insulating film 2104 is formed so as to cover the gate electrode2108. The gate insulating film 2104 is formed using a silicon nitridefilm, a silicon oxide film, a stacked layer structure thereof, or thelike. An amorphous semiconductor film is formed over the gate insulatingfilm 2104. Although a material of the amorphous semiconductor film isnot limited, the amorphous semiconductor film is preferably formed ofsilicon, a silicon-germanium (SiGe) alloy, or the like. Next, aconductive layer is formed over the amorphous semiconductor film. As theconductive layer, an amorphous silicon film containing phosphorus can beused, for example. The shapes of the amorphous semiconductor film andthe conductive layer are processed using a mask formed by aphotolithography method or the like so as to form an island-shapedamorphous semiconductor film and an island-shaped conductive layer.These are generally a semiconductor layer 2103 containing silicon as amain component.

A conductive layer is formed to be stacked over the semiconductor layer2103 and the shape thereof is processed using a mask formed by aphotolithography method or the like so as to form a drain electrode2109.

The conductive layer of the semiconductor layer 2103 is etched using thedrain electrode 2109 or the like as a mask, and thereby a source and adrain are separated. Such a structure is generally referred to as achannel etch type.

The drain electrode 2109 corresponds to the wiring 401 in FIGS. 4 and 6and the electrode 705 in FIGS. 7A, 7B, 8A, and 8B.

An insulating film 2102 is formed thereover. The insulating film 2102 ispreferably formed of a silicon nitride film since a silicon nitride filmcan prevent various impurities from entering the transistor. Note that asilicon oxide film or a stacked layer film including a silicon oxidefilm may be used.

Next, an insulating film 2107 is formed to absorb unevenness of thewiring and the like to be made even. The insulating film 2107 is madeusing an organic film such as acrylic or polyimide. A photosensitivematerial may be used as well.

The insulating film 2107 and the insulating film 2102 correspond to theinsulating film 107 in FIGS. 1A to 1C, 2A to 2C and 3A and 3B.

Next, a contact hole is formed in the insulating film 2102 and theinsulating film 2107. A conductive film is formed thereover.

An electrode 2106 in FIG. 21 corresponds to the conductive film 106 a inFIGS. 2C, and 4 to 6. An electrode 2105 in FIG. 21 corresponds to theconductive film 105 b in FIGS. 2C, and 4 to 6.

The electrode 2106 is a part of a pixel electrode and is a transparentelectrode which transmits light. The electrode 2105 is a part of a pixelelectrode and is a reflective electrode which reflects light. An entireunder surface of the reflective electrode is in contact with a topsurface of the transparent electrode.

As for the transparent electrode, for example, an indium tin oxide (ITO)film in which tin oxide is mixed in indium oxide, an indium tin siliconoxide (ITSO) film in which silicon oxide is mixed in indium tin oxide(ITO), an indium zinc oxide (IZO) film in which zinc oxide is mixed inindium oxide, a zinc oxide film, a tin oxide film, or the like can beused. Note that IZO is a transparent conductive material formed by asputtering method using a target in which 2 to 20 wt % of zinc oxide(ZnO) is mixed in ITO. However, the invention is not limited to this.

As for the reflective electrode, for example, Ti, Mo, Ta, Cr, W, Al, Nd,Cu, Ag, Au, Pt, Nb, Si, Zn, Fe, Ba, Ge, or the like, an alloy thereof,or the like can be used. A two-layer structure where Al is stacked withTi, Mo, Ta, Cr or W; or a three-layer structure where a layer of Al isinterposed between layers of a metal such as Ti, Mo, Ta, Cr, or W may beemployed.

The conductive film 2105 and the conductive film 2106 are formed by themethod described in Embodiment Modes 1 and 2.

Although not shown in the figure, an alignment film is often formed overthe conductive film 2105 and the conductive film 2106.

Concerning the opposite electrode 2114, the insulating film 2113, theplanarizing film 2112, the black matrix 2115, the color filter 2116, theopposite substrate 2111 and the liquid crystal layer 2110, although theyare similar to those described in Embodiment Modes 1 to 4, descriptionis made as an example.

Note that although the reflective electrode is not provided withunevenness in the reflection portion 920 in FIG. 21, unevenness may beformed as shown in FIGS. 5 and 6. This case is shown in FIG. 22.Unevenness may be formed by the method described in FIGS. 7A and 7B.Light can be diffused by unevenness 2201 and a contact hole 2201 a.

Note that light scattering particles may be mixed in films 2113 and 2213for adjusting a thickness. Therefore, light is scattered and luminancecan be improved. The light scattering particles are formed of a materialhaving a refractive index different from that of a cell gap adjustingfilm and formed from a resin material having a light transmittingproperty. A film for adjusting a cell gap may be formed so as to containsuch light scattering particles.

Note that although a thickness adjusting film is provided on theopposite substrate side in FIGS. 21 and 22, the invention is not limitedto this. The thickness adjusting film may be provided on a side where atransistor is formed. This case is shown in FIG. 23. Note that FIG. 21may be combined with FIG. 22. An example of this case is shown in FIG.24. A depressed portion 2301 corresponds to the depressed portion 801 inFIG. 8. As described above, the depressed portion 2301 is provided inthe transmission portion 921; therefore, a cell gap in the transmissionportion 921 can be made larger than a cell gap in the reflection portion920.

Note that although in FIG. 23, a part of an insulating film 2107 a isremoved in order that the depressed portion 2301 is formed, theinvention is not limited to this. Other insulating films may also beremoved. For example, a part of the insulating film 2102 as well as theinsulating film 2107 a may be removed. FIG. 52 shows the case where apart of a gate insulating film 2104 e and a substrate 2101 e are removedas well. Therefore, a difference in cell gaps between the reflectionportion 920 and the transmission portion 921 can be easily made. Aninsulating film 2102 e, the gate insulating film 2104 e, the substrate2101 e, and the like may be formed from a film having a similarcomponent in some cases; therefore, a depressed portion 2301 e can beformed more deeply.

Note that although both the depressed portion and the thicknessadjusting film are formed in FIG. 24, the invention is not limited tothis. One of them may be formed. When both of them are provided, athickness can be controlled by both of them; therefore, each thicknessis not required to be made very large, which leads to easymanufacturing.

Note that unevenness may be formed using a contact hole. This case isshown in FIG. 25. Unevenness is formed using a contact hole 2501 whichis provided in a part where the electrode 2106 is not connected to thedrain electrode 2109. A plurality of contact holes 2501 are formed inorder that surfaces of a wiring and an electrode are made uneven, butnot in order to connect wirings. Note that in the contact hole 2501,similarly in a contact hole 2201 a, the electrode 2106 may be in contactwith the drain electrode 2109.

Note that the depressed portion 2301 may be provided in the case of FIG.25.

Note that although a channel etch type transistor is used in FIGS. 21 to25, the invention is not limited to this. A channel protective typetransistor may be used. As an example, FIG. 26 shows a cross sectionalview when a channel protective type transistor is used in the case ofFIG. 21. A channel protective film 2601 is formed over a semiconductorlayer 2603 a in which a channel is formed. A semiconductor layer and aconductive film (a drain electrode, a source signal line or the like)2603 b containing phosphorus is formed thereover. A channel protectivetype transistor can be applied to the case of FIGS. 22 to 25 and 49.

A TFT including the channel protective film 2601 has the followingeffects. The semiconductor layer 2603 a can be formed thin since thereis no fear that the semiconductor layer is etched, and characteristicsof the TFT can be improved. Thus, a large current can be supplied to theTFT and signal writing time can be shortened, which is preferable.

Note that although the insulating film 2107 is formed over theinsulating film 2102 in FIGS. 21 to 26 and 49, the invention is notlimited to this. The case where planarization is not required can alsobe realized. FIG. 27 shows a cross sectional view of this case. By notforming the insulating film 2107, the number of steps can be reduced andcost can be reduced. Note that in the case of FIG. 27, a surface of thereflective electrode may be uneven, a thickness adjusting film or adepressed portion may be provided so as to adjust a cell gap, orunevenness of the reflective electrode may be formed using a contacthole.

As described above, there are a plurality of methods for each ofpresence of unevenness, a forming method of unevenness, and an adjustingmethod of a cell gap (thickness adjusting is performed on an oppositesubstrate side or a TFT substrate side). Therefore, any of them may beselected and combined.

Note that this embodiment mode shows an example in the case wheredescription in Embodiment Modes 1 to 4 is concretely realized and a partthereof is described in detail. Therefore, the description in EmbodimentModes 1 to 4 can be applied to this embodiment mode or combined withthis embodiment mode.

In addition, description is made with reference to various drawings inthis embodiment mode. One drawing consists of various components.Therefore, another structure can be made by combining each of thecomponents from each drawing.

Embodiment Mode 6

Description has been made mainly with reference to cross sectional viewsso far. In this embodiment mode, a top plan view is described.

FIG. 28 is a top plan view which can be applied to the cases in FIGS. 9and 47. FIG. 28 shows one pixel (one color element). A semiconductorlayer 2803 a is formed, over which a gate wiring 2808 a and a capacitorline 2808 b are formed. A transistor is formed by a gate electrode whichis a film formed continuously with the gate wiring 2808 a and is formedover the semiconductor layer 2803 a. The semiconductor layer 2803 a isprovided below the capacitor line 2808 b. A storage capacitor is formedby the capacitor line 2808 b and the semiconductor layer 2803 a. Acapacitor is formed by upper and lower electrodes with a gate insulatingfilm interposed therebetween. In this case, phosphorus or boron may beadded, or not, to a region of the semiconductor layer 2803 a whichfunctions as an electrode of the capacitor. When phosphorus or boron isnot added, a high voltage is applied to the capacitor line 2808 b. Whenphosphorus or boron is added, the capacitor line 2808 b is oftenelectrically connected to an opposite electrode. Therefore, the numberof wirings can be reduced.

A source signal line 2809 a and a drain electrode 2809 b are formedthereover and connected to the semiconductor layer 2803 a through acontact hole.

Note that the drain electrode 2809 b may be largely provided so as tomake a region which is overlapped with the capacitor line 2808 b large;therefore, a capacitance value of the storage capacitor can beincreased.

A transparent electrode 2806 is formed thereover and connected to thedrain electrode 2809 b through a contact hole. A reflective electrode2803 b is formed thereover.

The reflective electrode 2803 b is formed over the transistor and thestorage capacitor. Therefore, an aperture ratio of the transmissionportion can be increased and layout can be efficiently designed.

Note that although the capacitor line 2808 b is provided, the inventionis not limited to this. Instead of the capacitor line 2808 b, a gatesignal line of one preceding row may be used. That is, a potential ofthe gate signal line of one preceding row is constant in a non-selectedstate, thereby functioning as a storage capacitor line.

The storage capacitor is provided at the center part of a pixelelectrode in FIG. 29, while the storage capacitor is provided in thevicinity of the transistor in FIG. 28. Therefore, a plurality oftransmission regions can be provided in one pixel. Accordingly, aplurality of regions in which alignment states of liquid crystalmolecules are different from each other can exist, and a multi-domainstructure can be easily realized. A wide viewing angle can be obtainedby having a multi-domain structure.

FIG. 30 shows the case where the reflective electrode is provided withunevenness 3001 with respect to the case of FIG. 27. This corresponds toFIGS. 10 and 13. The reflective electrode is provided with unevenness,so that light is scattered and luminance can be improved.

Similarly, FIG. 31 shows the case where the reflective electrode isprovided with the unevenness 3001 with respect to the case of FIG. 29where the storage capacitor is provided at the center part of the pixelelectrode. The reflective electrode is provided with the unevenness, sothat light is scattered and luminance can be improved. Further, aplurality of regions in which alignment states of liquid crystalmolecules are different from each other can exist, and a multi-domainstructure can be easily realized. By having a multi-domain structure,light transmittance can be prevented from decreasing when seen at aspecific angle, and a wide viewing angle can be obtained.

Next, FIG. 32 shows the case where a depressed portion 3201 is formed asshown in FIG. 11. By forming the depressed portion 3201, a cell gap inthe reflection portion and a cell gap in the transmission portion can beeasily differentiated; therefore, visibility can be improved and animage with less color unevenness can be displayed with appropriate grayscales. Further, cell gap adjustment can be realized simultaneously on aside of a substrate where the transistor, the capacitor, the wiring, andthe like are provided; therefore, cell gap adjustment can be realizedwith a small number of steps and at low cost.

Similarly, FIG. 33 shows the case where unevenness 3201 a and unevenness3201 b are formed with respect to the case of FIG. 29 where the storagecapacitor is provided at the center part of the pixel electrode.

In FIGS. 28 to 33, description is made of the case where a pixelelectrode is provided all over each pixel. This mainly corresponds tothe case of being used as the TN liquid crystal.

As shown in FIGS. 18 and 19, the pixel electrode can be provided with aslit or divided so as to be arranged at intervals.

FIG. 34 is a top plan view, which corresponds to the MVA mode, the PVAmode, or the like by providing the pixel electrode with a slit or bydividing the pixel electrode so as to be arranged at intervals. Slits3401 a, 3401 b, 3401 c, 3401 d, and the like are formed both in thetransmission region and the reflection region, and thereby a directionof tilt of liquid crystal molecules can be determined.

A storage capacitor portion is provided below the reflection portion;therefore, an aperture ratio of the transmission portion can beincreased and layout can be efficiently designed.

The reflection portion and the storage capacitor are provided in thecenter portion of the pixel electrode and transmission portions areprovided adjacent thereto; therefore, a plurality of transmissionportions can be provided in one pixel. Accordingly, a plurality ofregions in which alignment states of liquid crystal molecules aredifferent from each other can exist, and a multi-domain structure can beeasily realized. By having a multi-domain structure, light transmittancecan be prevented from decreasing when seen at a specific angle, and awide viewing angle can be obtained.

FIG. 35 shows the case where unevenness 3001 is formed in thetransmission portion. The reflective electrode is provided with theunevenness, so that light is scattered and luminance can be improved.

As described above, the structure where the pixel electrode is providedwith a slit or divided so as to be arranged at intervals can also beapplied to FIGS. 28 to 33.

Note that a method of forming a slit is not limited to FIGS. 34 and 35,and various ways of arrangement can be employed.

Although FIGS. 28 to 35 show examples in the case of using a transistorwith a top gate structure, the invention is not limited to these and astructure other than these can be employed. Next, an example of using atransistor with an inversed staggered structure is shown.

FIG. 36 corresponds to FIG. 21. A gate wiring 3608 a and a capacitorline 3608 b are formed. A semiconductor layer 3603 is formed thereover.A transistor is formed by a gate electrode which is a film formedcontinuously with the gate wiring 3608 a and is formed below thesemiconductor layer 3603. A source signal line 3609 a and a drainelectrode 3619 b are formed thereover. The drain electrode 3619 b isformed over the capacitor line 3608 b, where the storage capacitor isformed. A capacitor is formed by upper and lower electrodes with a gateinsulating film interposed therebetween. A transparent electrode 3606 isformed thereover and connected to the drain electrode 3619 b through acontact hole. A reflective electrode 3605 is formed thereover.

The reflective electrode 3605 is formed over the transistor and thestorage capacitor. Therefore, an aperture ratio of the transmissionportion can be increased and layout can be efficiently designed.

Although the storage capacitor is provided in the vicinity of thetransistor in FIG. 36, the storage capacitor may be provided at thecenter part of the pixel electrode. Therefore, a plurality oftransmission portions can be provided in one pixel. Accordingly, aplurality of regions in which alignment states of liquid crystalmolecules are different from each other can exist, and a multi-domainstructure can be easily realized. By having a multi-domain structure,light transmittance can be prevented from decreasing when seen at aspecific angle, and a wide viewing angle can be obtained.

FIG. 37 shows the case where the reflective electrode is provided withunevenness 3701 with respect to FIG. 36. By forming unevenness over thereflective electrode, light is scattered and luminance can be improved.

FIG. 38 shows the case where a depressed portion 3801 is formed as shownin FIG. 23. By forming the depressed portion 3801, a cell gap in thereflection portion and a cell gap in the transmission portion can beeasily differentiated; therefore, visibility can be improved and animage with less color unevenness can be displayed with appropriate grayscales.

In FIGS. 36 to 38, description is made of the case where a pixelelectrode is provided all over each pixel. This mainly corresponds tothe case of being used as the TN liquid crystal.

As shown in FIGS. 18 and 19, the pixel electrode can be provided with aslit or divided so as to be arranged at intervals.

FIG. 39 is a top plan view, which corresponds to the MVA mode, the PVAmode, or the like by providing the pixel electrode with a slit or bydividing the pixel electrode so as to be arranged at intervals. Slits3901 a, 3901 b, 3901 c, 3901 d, and the like are formed both in thetransmission region and the reflection region, and thereby a directionof inclination of liquid crystal molecules can be determined.

A storage capacitor portion is provided below the reflection portion;therefore, an aperture ratio of the transmission portion can beincreased and layout can be efficiently designed.

The reflection portion and the storage capacitor are provided in thecenter portion of the pixel electrode and transmission portions areprovided adjacent thereto; therefore, a multi-domain structure can beeasily realized. By having a multi-domain structure, light transmittancecan be prevented from decreasing when seen at a specific angle, and awide viewing angle can be obtained.

Note that unevenness may be formed in the reflection portion (over areflective electrode 3605 a).

Note that the slits in FIG. 39 are wave-shaped, and thereby liquidcrystal molecules can be more easily controlled.

As described above, the structure where the pixel electrode is providedwith a slit or divided so as to be arranged at intervals can also beapplied to other top plan views.

Note that a method of forming a slit is not limited to FIG. 39, andvarious ways of arrangement can be employed.

Note that this embodiment mode shows an example in the case where thedescription in Embodiment Modes 1 to 5 is concretely realized and a partthereof is described in detail. Therefore, the description in EmbodimentModes 1 to 5 can be applied to this embodiment mode or combined withthis embodiment mode.

In addition, description is made with reference to various drawings inthis embodiment mode. One drawing consists of various components.Therefore, another structure can be made by combining each of thecomponents from each drawing.

Embodiment Mode 7

In this embodiment mode, description is made of the light exposure maskused in Embodiment Modes 1 to 6, with reference to FIGS. 20A to 20D.FIGS. 20A to 20C are top plan views of the light shielding portion 101 aand the semi-transmission portion 101 b of the light exposure mask shownin FIGS. 1A to 1C, 3A, 3B, 7A, 7B, and 8A and 8B. A width of a lightshielding portion 101 a of the light exposure mask is denoted by t1, anda width of a semi-transmission portion 101 b thereof is denoted by t2.

The semi-transmission portion 101 b can be provided with a diffractiongrating pattern. Each of FIGS. 20A and 20B shows a diffraction gratingpattern including a slit portion formed by a plurality of slits which isequal to or smaller than a resolution limit of a light exposureapparatus. The diffraction grating pattern is a pattern in which atleast one pattern such as a slit or a dot is arranged. When a pluralityof patterns such as slits or dots is arranged, the patterns may bearranged periodically or aperiodically. By using a minute pattern whichis equal to or smaller than a resolution limit, a substantial amount ofexposure can be changed and a thickness of a resist exposed to lightafter development can be adjusted.

The slit of the slit portion may be extended in a direction parallel toone side of a light shielding portion 303 like a slit portion 301; or ina direction perpendicular to one side of the light shielding portion 303like a slit portion 302. The slit of the slit portion may be extended inan oblique direction with respect to one side of the light shieldingportion 303. Note that a resist used for this photolithography step ispreferably a positive type resist.

As another example of the semi-transmission portion, FIG. 20C shows anexample where a semi-transmission film 2004 having a function ofreducing intensity of exposure light is provided. As thesemi-transmission film, MoSi, MoSiO, MoSiON, CrSi, or the like as wellas MoSiN can be used. A light exposure method using a light exposuremask including a semi-transmission portion is referred to as a half-tonelight exposure method.

When the light exposure masks shown in FIGS. 20A to 20C are irradiatedwith exposure light, the light intensity is zero in the light shieldingportion 303 and the light intensity is 100% in a light transmittingportion 305. On the other hand, the intensity of light passing throughthe semi-transmission portion having a light intensity reductionfunction formed by the slit portion 301 or 302, or the semi-transmissionfilm 2004, can be adjusted in the range of 10 to 70%. FIG. 20D shows atypical example of a light intensity distribution. When thesemi-transmission portion is a diffraction grating pattern, adjustmentof the intensity of light passing through the semi-transmission portioncan be realized by adjustment of the pitch and the slit width of theslit portions 301 and 302.

This embodiment mode can be freely combined with Embodiment Modes 1 to6.

Embodiment Mode 8

Description is made of a pixel circuit of the invention. In FIG. 45,pixels 50001 are arranged in matrix in a pixel array 50000. The pixel50001 is connected to a source signal line 50002 to which a video signalis inputted and a gate signal line 50003 to which a gate signal isinputted. A transistor 50004 is controlled by using these signals sothat a video signal is inputted to a liquid crystal C_(LC) and a storagecapacitor C_(S). The storage capacitor C_(S) is connected to a storagecapacitor line 50005. Light transmittance of the liquid crystal C_(LC)is changed in accordance with the video signal; therefore, an image isdisplayed.

As shown in FIG. 46, at least the pixel array 50000 is provided over aglass substrate 60000. A gate signal line driver circuit 60001 fordriving the gate signal line and a source signal line driver circuit60002 for supplying a video signal to the source signal line may beprovided in some cases. Both of them may be provided in some cases andone of them may be provided in other cases.

The source signal line driver circuit 60002 includes a shift register, asampling switch, a latch circuit, a D/A converter circuit, or the like;however, the invention is not limited to this. Only a sampling switchmay be provided and a shift register and the like are not provided insome cases.

Note that this embodiment mode shows an example in the case where thedescription in Embodiment Modes 1 to 7 is concretely realized and a partthereof is described in detail. Therefore, the description in EmbodimentModes 1 to 7 can be applied to this embodiment mode or combined withthis embodiment mode.

In addition, description is made with reference to various drawings inthis embodiment mode. One drawing consists of various components.Therefore, another structure can be made by combining each of thecomponents from each drawing.

Embodiment Mode 9

A structure example of a mobile phone in which a display device of theinvention is included in a display portion is described with referenceto FIG. 40.

A display panel 5410 is detachably incorporated into a housing 5400. Ashape and size of the housing 5400 can be changed as appropriate inaccordance with a size of the display panel 5410. The housing 5400 whichfixes the display panel 5410 is fit into a printed circuit board 5401and assembled as a module.

The display panel 5410 is connected to the printed circuit board 5401through an FPC 5411. A speaker 5402, a microphone 5403, atransmission/reception circuit 5404, and a signal processing circuit5405 including a CPU, a controller, and the like are formed over theprinted circuit board 5401. Such a module is combined with an input unit5406 and a battery 5407, and incorporated into chassis 5409 and 5412. Apixel portion of the display panel 5410 is provided so as to be seenfrom an open window formed in the chassis 5412.

The display panel 5410 may be formed in such a manner that the pixelportion and a part of peripheral driver circuits (a driver circuit witha low operating frequency among a plurality of driver circuits) areformed over the same substrate by using TFTs, while another part of theperipheral driver circuits (a driver circuit with a high operatingfrequency among the plurality of driver circuits) is formed over an ICchip, which may be mounted on the display panel 5410 by COG (Chip OnGlass). Alternatively, the IC chip may be connected to a glass substrateby TAB (Tape Automated Bonding) or by using a printed circuit board.Note that FIG. 41A shows an example of a structure of a display panel inwhich a part of peripheral driver circuits and a pixel portion areformed over a substrate, while an IC chip where another part of theperipheral driver circuits is formed is mounted on the substrate by COGor the like. According to such a structure, power consumption of thedisplay device can be reduced, and operation time of a mobile phone percharge can be extended. In addition, cost reduction of a mobile phonecan be achieved.

In addition, time to write a signal to pixels in one row can beshortened by converting an impedance of the signal set to a scan line ora signal line by a buffer. Therefore, a high-definition display devicecan be provided.

In order to further reduce power consumption, a pixel portion may beformed over a substrate by using TFTs and all the peripheral circuitsmay be formed over an IC chip, which may be mounted on the display panelby COG (Chip On Glass) or the like.

By using the display device of the invention, a high-contrast image canbe obtained.

Note that the structure shown in this embodiment mode is an example of amobile phone; therefore, the display device of the invention is notlimited to the mobile phone with the aforementioned structure and can beapplied to mobile phones with various structures.

Note that the description in this embodiment mode can be freely combinedwith that in Embodiment Modes 1 to 8.

In addition, description is made with reference to various drawings inthis embodiment mode. One drawing consists of various components.Therefore, another structure can be made by combining each of thecomponents from each drawing.

Embodiment Mode 10

FIG. 42 shows a liquid crystal module combined with a display panel 5701and a circuit substrate 5702. The display panel 5701 includes a pixelportion 5703, a scan line driver circuit 5704, and a signal line drivercircuit 5705. For example, a control circuit 5706, a signal dividingcircuit 5707, and the like are formed over the circuit substrate 5702.The display panel 5701 and the circuit substrate 5702 are connected by aconnection wiring 5708. An FPC or the like can be used for theconnection wiring.

The display panel 5701 may be formed in such a manner that a pixelportion and a part of peripheral driver circuits (a driver circuit witha low operating frequency among a plurality of driver circuits) areformed over the same substrate by using TFTs, while another part of theperipheral driver circuits (a driver circuit with a high operatingfrequency among the plurality of driver circuits) is formed over an ICchip, which may be mounted on the display panel 5701 by COG (Chip OnGlass) or the like. Alternatively, the IC chip may be mounted on thedisplay panel 5701 by TAB (Tape Automated Bonding) or by using a printedcircuit board. Note that FIG. 41A shows an example of a structure inwhich a part of peripheral driver circuits and a pixel portion areformed over a substrate, while an IC chip where another part of theperipheral driver circuits is formed is mounted on the substrate by COGor the like. By using such a structure, power consumption of the displaydevice can be reduced, and operation time of a mobile phone per chargecan be extended. In addition, cost reduction of a mobile phone can beachieved.

In addition, time to write a signal to pixels in one row can beshortened by converting an impedance of a signal set to a scan line or asignal line by a buffer. Therefore, a high-definition display device canbe provided.

In order to further reduce power consumption, a pixel portion may beformed over a glass substrate with TFTs and all the signal line drivercircuits may be formed over an IC chip, which may be mounted on thedisplay panel by COG (Chip On Glass).

Note that it is preferable that a pixel portion be formed over asubstrate by using TFTs and all the peripheral driver circuits be formedover an IC chip, which be mounted on the display panel by COG (Chip OnGlass). FIG. 41B shows an example of a structure where a pixel portionis formed over a substrate and an IC chip in which a signal line drivercircuit is formed is mounted on the substrate by COG or the like.

A liquid crystal television receiver can be completed with this liquidcrystal module. FIG. 43 is a block diagram showing a main structure ofthe liquid crystal television receiver. A tuner 5801 receives a videosignal and an audio signal. The video signal is processed by a videosignal amplifier circuit 5802; a video signal processing circuit 5803which converts a signal outputted from the video signal amplifiercircuit 5802 to a color signal corresponding to each color of red,green, and blue; and a control circuit 5706 which converts the videosignal to input specifications of a driver circuit. The control circuit5706 outputs signals to each of a scan line side and a signal line side.When performing digital drive, the signal dividing circuit 5707 may beprovided on the signal line side so that the inputted digital signal isdivided into m signals to be supplied.

Among the signals received by the tuner 5801, an audio signal istransmitted to an audio signal amplifier circuit 5804, and an outputthereof is supplied to a speaker 5806 through an audio signal processingcircuit 5805. A control circuit 5807 receives control data on areceiving station (receive frequency) and volume from an input portion5808, and transmits the signal to the tuner 5801 and the audio signalprocessing circuit 5805.

A television receiver can be completed by incorporating a liquid crystalmodule into a housing. A display portion is formed by the liquid crystalmodule. In addition, a speaker, a video input terminal, and the like areprovided as appropriate.

Needless to say, the invention is not limited to a television receiverand can be applied to various uses such as a monitor of a personalcomputer, an information display board at a train station or an airport,and an advertising display board on the street, specifically as alarge-area display medium.

As described above, a high-contrast image can be obtained by using thedisplay device of the invention.

Note that the description in this embodiment mode can be freely combinedwith that in Embodiment Modes 1 to 9.

In addition, description is made with reference to various drawings inthis embodiment mode. One drawing consists of various components.Therefore, another structure can be made by combining each of thecomponents from each drawing.

Embodiment Mode 11

The invention can be applied to various electronic apparatuses.Specifically, the invention can be applied to a display portion of anelectronic apparatus. As such an electronic apparatus, a camera such asa video camera and a digital camera, a goggle type display, a navigationsystem, an audio reproducing device (a car audio, an audio componentstereo, and the like), a computer, a game machine, a portableinformation terminal (a mobile computer, a mobile phone, a portable gamemachine, an electronic book, and the like), an image reproducing deviceprovided with a recording medium (specifically, a device whichreproduces a recording medium such as a digital versatile disc (DVD) andhas a display device for displaying the reproduced image), and the likeare taken as examples.

FIG. 44A shows a display device, which includes a chassis 35001, asupporting base 35002, a display portion 35003, speaker portions 35004,a video input terminal 35005, and the like. The display device of theinvention can be applied to the display portion 35003. Note that thedisplay device includes all information display devices such as thosefor a personal computer, TV broadcasting reception, and advertisementdisplay. A display device which uses the display device of the inventionfor the display portion 35003 can provide a high-contrast image.

FIG. 44B shows a camera, which includes a main body 35101, a displayportion 35102, an image receiving portion 35103, operating keys 35104,an external connecting port 35105, a shutter 35106, and the like.

A digital camera in which the invention is applied to the displayportion 35102 can provide a high-contrast image.

FIG. 44C shows a computer, which includes a main body 35201, a chassis35202, a display portion 35203, a keyboard 35204, an external connectingport 35205, a pointing device 35206, and the like. A computer in whichthe invention is applied to the display portion 35203 can provide ahigh-contrast image.

FIG. 44D shows a mobile computer, which includes a main body 35301, adisplay portion 35302, a switch 35303, operating keys 35304, an infraredport 35305, and the like. A mobile computer in which the invention isapplied to the display portion 35302 can provide a high-contrast image.

FIG. 44E shows a portable image reproducing device provided with arecording medium (specifically, a DVD player), which includes a mainbody 35401, a chassis 35402, a display portion A 35403, a displayportion B 35404, a recording medium (such as DVD) reading portion 35405,an operating key 35406, a speaker portion 35407, and the like. Thedisplay portion A 35403 mainly displays image data, while the displayportion B 35404 mainly displays text data. An image reproducing devicein which the invention is applied to the display portion A 35403 and thedisplay portion B 35404 can provide a high-contrast image.

FIG. 44F shows a goggle type display, which includes a main body 35501,a display portion 35502, an arm portion 35503, and the like. A goggletype display in which the invention is applied to the display portion35502 can provide a high-contrast image.

FIG. 44G shows a video camera, which includes a main body 35601, adisplay portion 35602, a chassis 35603, an external connecting port35604, a remote controller receiving portion 35605, an image receivingportion 35606, a battery 35607, an audio input portion 35608, operatingkeys 35609, an eyepiece portion 35610, and the like. A video camera inwhich the invention is applied to the display portion 35602 can providea high-contrast image.

FIG. 44H shows a mobile phone, which includes a main body 35701, achassis 35702, a display portion 35703, an audio input portion 35704, anaudio output portion 35705, an operating key 35706, an externalconnecting port 35707, an antenna 35708, and the like. A mobile phone inwhich the invention is applied to the display portion 35703 can providea high-contrast image.

As described above, the applicable range of the invention is so widethat the invention can be applied to electronic apparatuses of variousfields. In addition, the electronic apparatuses in this embodiment modemay use a display device with any of the structures described inEmbodiment Modes 1 to 13.

This application is based on Japanese Patent Application serial No.2005-378778 filed in Japan Patent Office on Dec. 28, 2005, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A liquid crystal display device comprising: atransistor over a first substrate, the transistor comprising a firstchannel formation region and a second channel formation region in asemiconductor film; a first insulating film over the semiconductor film;a gate wiring over the first insulating film; a first conductive filmover the first substrate; a second insulating film over the gate wiringand the first conductive film; a source line over and in contact withthe second insulating film; a drain electrode over and in contact withthe second insulating film; a third insulating film over and in contactwith the source line; a second conductive film over and in contact withthe third insulating film, the second conductive film comprising indiumtin oxide; a third conductive film over and in contact with the secondconductive film, the third conductive film comprising aluminum; a fourthconductive film over the second conductive film; a liquid crystal layerover the third conductive film; and a second substrate over the liquidcrystal layer, wherein the second conductive film comprises a firstregion which is overlapped with the third conductive film and a secondregion which is not overlapped with the third conductive film, whereinthe first region includes a region which overlaps the first conductivefilm with the third insulating film interposed therebetween, wherein thesecond region overlaps with the first substrate with the thirdinsulating film interposed therebetween, wherein the second region has alarger area than the first region, wherein the third conductive filmoverlaps the first conductive film along a long axis direction thereof,wherein the semiconductor film comprises a third region whose long axisis provided along a long axis direction of the gate wiring and a fourthregion whose long axis is provided along a long axis direction of thesource line, wherein the fourth region includes a region which isoverlapped with the first region, and wherein the third region includesa fifth region which is not overlapped with the third conductive film.2. The liquid crystal display device according to claim 1, wherein thesemiconductor film is an oxide semiconductor film which comprises In andZn.
 3. The liquid crystal display device according to claim 1, whereinthe second insulating film comprises silicon nitride, and wherein thethird insulating film comprises an organic material.
 4. The liquidcrystal display device according to claim 1, wherein the semiconductorfilm comprises polycrystalline silicon.
 5. A liquid crystal displaydevice comprising: a transistor over a first substrate, the transistorcomprising a first channel formation region and a second channelformation region in a semiconductor film; a first insulating film overthe semiconductor film; a gate wiring over the first insulating film; afirst conductive film over the first substrate; a second insulating filmover the gate wiring and the first conductive film; a source line overand in contact with the second insulating film; a drain electrode overand in contact with the second insulating film; a third insulating filmover and in contact with the source line; a second conductive film overand in contact with the third insulating film, the second conductivefilm comprising indium tin oxide; a third conductive film over and incontact with the second conductive film, the third conductive filmcomprising aluminum; a fourth conductive film over the second conductivefilm; a liquid crystal layer over the third conductive film; and asecond substrate over the liquid crystal layer, wherein the secondconductive film comprises a first region which is overlapped with thethird conductive film and a second region which is not overlapped withthe third conductive film, wherein the first region includes a regionwhich overlaps the first conductive film with the second insulating filmand the third insulating film interposed therebetween, wherein thesecond region overlaps with the first substrate with the thirdinsulating film interposed therebetween, wherein the second region has alarger area than the first region, wherein the third conductive filmoverlaps the first conductive film along a long axis direction thereof,wherein the semiconductor film comprises a third region whose long axisis provided along a long axis direction of the gate wiring and a fourthregion whose long axis is provided along a long axis direction of thesource line, wherein the fourth region includes a region which isoverlapped with the first region, and wherein the third region includesa fifth region which is not overlapped with the third conductive film.6. The liquid crystal display device according to claim 5, wherein thesemiconductor film is an oxide semiconductor film which comprises In andZn.
 7. The liquid crystal display device according to claim 5, whereinthe second insulating film comprises silicon nitride, and wherein thethird insulating film comprises an organic material.
 8. The liquidcrystal display device according to claim 5, wherein the semiconductorfilm comprises polycrystalline silicon.